Pumps are conventionally used in hydraulic systems in order to pressurize the hydraulic fluid within the hydraulic conduit lines. The pump generates a dynamic fluctuation of the hydraulic pressure over the mean static pressure of work performed by the pressurized hydraulic fluid. This hydraulic pressure fluctuation is known colloquially in the art as “ripple” and generates a very high amplitude sound pressure noise at high frequency. The main path of vibroacoustic energy flow is fluid-borne. Such fluid-borne vibroacoustic energy can be manifested by audible and objectionable noise which also can cause fatigue wear of hydraulic system components.
It is therefore conventional practice to employ an attenuator to minimize the vibroacoustic energy flow in hydraulic systems. Due to design simplicity and low pressure losses, it is typical to employ a reflective (or reactive) attenuator so as to attenuate ripple noise in pump-activated hydraulic systems. The basic principle of a reflective attenuator is to reflect the fluid pulse back toward the source, e.g., the pump in a pump-activated hydraulic system. Typical known expansion reflective attenuators include expansion chambers, Helmoltz resonators and lateral branches (e.g., as disclosed in NASA Technical Memorandum X-2787, December 1973, the entire content of which is expressly incorporated hereinto by reference). In all such types of reflective attenuators, the attenuator cavity is tuned to a specific frequency based on the fluid pulse wavelength. Helmoltz resonator and lateral branch resonators will have a narrow range of optimum performance.
The use of reflective attenuators can lead to between about 20 dB to about 40 dB decrease in the frequency of interest. The principle disadvantages of currently known reflective attenuators include (i) a narrow frequency range of optimum performance (e.g., for non-constant speed pumps only a certain operational condition can be optimized such that the performance of the attenuator is highly affected should the operational condition be at variance to the predetermined condition for which the attenuator is tuned), and (ii) the occurrence of substantial back pressure (e.g., the reflected pulse back to the pump outlet can lead to accelerated component wear).
A hydraulic attenuator has also been proposed by U.S. Pat. No. 6,155,378 (the entire content of which is expressly incorporated hereinto by reference). The attenuator suggested by the US '378 patent functions as a dissipater and has the characteristic of broadband actuation of frequency but without high performance at any specific frequency range. In order to achieve this result, the US '378 patent proposes a multi-chamber solution to attenuate fluid-borne noise by dividing an attenuator conduit hose or pipe assembly serially into tuning chambers by a restrictor or other mechanism.
As can be appreciated, there still exists a need in this art to provide hydraulic attenuation of fluid-borne ripples which can function over a wider range of frequencies. It is towards fulfilling such need that the embodiments disclosed herein are directed.